It wasn't only buzzing before the humans, it had the right answer ready to go before the humans in most cases as well.
This is a HUGE assumption. We don't know how long it took for Watson to come up with an answer, and we don't know for the humans either. Jeopardy rules are such that you *cannot* buzz before the end of the question. The speed aspect was removed from the equation.
If you took out the buzzer limitation it would have been a much more interesting (but less fun to watch) competition. Imagine the category is state capitals, and the words "pelican state" are in the clue. That's all a good human would need to buzz, just the word pelican. If the human was anticipating a state nickname (and knew them all), the human could buzz before the moderator even said the word, hear the word as the buzzer is going off, then give the answer. What would it take to build Watson to do that? What if the computer had to listen to the words (and understand them) instead of being fed them electronically? That sort of timing, anticipation, and processing is a much greater challenge than what we saw and would also be immensely useful. If you wanted to build a robot that could listen to someone and respond, that is the sort of intelligence and speed you'd need.
The engineers who worked on the project did a great job...I'm just hoping there's more coming along the same lines.